Electrochemical double-cell plate and apparatus for exhaust emissions control

ABSTRACT

An electrochemical double-cell plate for exhaust emissions control is used to purify an oxygen-rich combustion waste gas and comprises a substrate made of a metal or an alloy and having a reducing capability; a solid-state oxide layer; a boundary layer; and a cathode layer. The solid-state oxide layer and the boundary layer cooperate to seal the substrate and respectively have a first compact microstructure and a second compact microstructure. The cathode layer completely covers the solid-state oxide layer, made of a porous material and having an oxidizing environment. The oxidizing environment and the reducing capability generate an electromotive force between the substrate and the cathode layer. The electromotive force drives sulfur oxides and nitrogen oxides of the oxygen-rich combustion waste gas to decompose into sulfur vapor, oxygen and nitrogen. An electrochemical apparatus using the same for exhaust emissions control is also disclosed.

FIELD OF THE INVENTION

The present invention relates to an electrochemical double-cell plateand apparatus, particularly to an electrochemical double-cell plate andapparatus for exhaust emissions control.

BACKGROUND OF THE INVENTION

The waste gas, which pollutes the air, includes nitrogen oxides(NO_(x)), sulfur oxides (SO_(x)), carbon monoxide (CO), hydrocarbons(HCs), and particulate matters (PMs). Researches show that sulfur oxidesin the waste gas emitted by motorcycles, automobiles, factories, powerplants seriously affect human health. Therefore, the industry andacademia have paid much effort to develop technologies for effectivelyeliminating sulfur oxides in waste gas.

The emission standard of motor vehicles is improving persistently.However, the continuously increasing motor vehicles still bring aboutmore and more serious air pollution. In a motor vehicle, the enginethereof burns fuel and converts chemical energy into mechanical energy.The burning process of fuel generates exhaust gases, including nitrogenoxides (NO_(x)), carbon monoxide (CO), hydrocarbons (HCs), andparticulate matters (PM), which would form photochemical smog, causeacid rain, damage the ecological environment and endanger human health.

Carbon monoxide comes from imperfect combustion. The capability ofcarbon monoxide to combine with hemoglobin to form carboxyhemoglobin(COHb) is 300 times higher than the capability of oxygen to combine withhemoglobin to form oxyhemoglobin (HbO₂). Therefore, too high aconcentration of carbon monoxide would degrade the capability ofhemoglobin to transport oxygen. Nitrogen oxides are generated by thecombination of nitrogen and oxygen and mainly in form of nitrogenmonoxide (NO) and nitrogen dioxide (NO₂). Under radiation of ultravioletray, nitrogen oxides are likely to react with hydrocarbons to form toxicphotochemical smog, which has a special odor, irritates eyes, harmsplants, and decreases atmospheric visibility. Further, nitrogen oxidesreact with humidity in the air to form nitric acid and nitrous acid,which are contributors to acid rain. Hydrocarbons may irritate therespiratory system even at a lower concentration and will affect thecentral nervous system at higher concentration. Besides, particulatematters may endanger health or even cause cancer.

Therefore, many nations, including EU, USA, Japan and Taiwan, haveregulated stricter emission standards for nitrogen oxides, carbonmonoxide, hydrocarbons (HCs) and particulate matters, such as (BINS ofUSA and EURO 6 of EU), which not only regulate the emission of harmfulexhaust gases but also encourage the manufacturers to develop, fabricateor use the newest pollution control technologies and apparatuses.

A U.S. Pat. No. 5,401,372 disclosed an “Electrochemical CatalyticReduction Cell for the Reduction of NO_(x) in an O₂-Containing ExhaustEmission”, which is dedicated to removing nitrogen oxides, wherein anelectrochemical catalytic reducing reaction and a vanadium pentaoxide(V₂O₅) catalyst convert nitrogen oxides into nitrogen. However, theprior-art device needs an electric source to power an electrochemicalcell. Therefore, the prior-art device consumes more power but cannoteliminate other harmful gases simultaneously.

A U.S. Pat. No. 9,028,764 disclosed an “Electro-Catalytic Honeycomb forExhaust Emissions Control”, which can purify waste gas via eliminatingnitrogen oxides, carbon monoxide, hydrocarbons (HCs) and particulatematters, wherein nitrogen oxides are decomposed into nitrogen andoxygen, and wherein carbon monoxide, hydrocarbons, and particulatematters are oxidized into water and carbon dioxide. Theelectro-catalytic honeycomb can eliminate several types of pollutants,neither consuming additional power nor using any reducing gas. However,the electro-catalytic honeycomb has higher fabrication cost. Besides,the electro-catalytic honeycomb is likely to be blocked while processingwaste gas containing a higher concentration of particles.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to solve the problemthat the conventional electro-catalytic honeycomb for exhaust emissionscontrol is expensive and likely to be blocked by particles whileprocessing waste gas containing a high concentration of dust.

In order to achieve the abovementioned objective, the present inventionproposes an electrochemical double-cell plate for exhaust emissionscontrol, which is used to purify an oxygen-rich combustion waste gas,and which comprises

a substrate made of a metal or an alloy and functioning as a reducingsubstrate, wherein the substrate has an outer surface, and wherein theouter surface has a top surface, a bottom surface opposite the topsurface, and a side surface joined with the top surface and the bottomsurface;

a solid-state oxide layer covering the top surface and the bottomsurface and having a first compact microstructure;

a boundary layer covering the side surface, having a second compactmicrostructure, and cooperating with the solid-state oxide layer to sealthe outer surface of the substrate; and

a cathode layer covering the solid-state oxide layer, made of a porousmaterial, contacting the oxygen-rich combustion waste gas, and having anoxidizing environment,

wherein the oxidizing environment and the reducing capability generatesan electromotive force between the substrate and the cathode layer andmake the cathode layer have a first reactive side and a second reactiveside respectively corresponding to the top surface and the bottomsurface of the substrate, and wherein the electromotive force enablessulfur oxides and nitrogen oxides of the oxygen-rich combustion wastegas to undertake decomposition reactions on the first reactive side andthe second reactive side to generate sulfur vapor, oxygen and nitrogen.

The present invention also proposes an electrochemical apparatus forexhaust emissions control, which is used to purify an oxygen-richcombustion waste gas, and which comprises

-   -   a plurality of the abovementioned electrochemical double-cell        plates for exhaust emissions control; and    -   a frame including an inlet allowing the oxygen-rich combustion        waste gas to flow into the electrochemical apparatus, an outlet        allowing the oxygen-rich combustion waste gas to flow out of the        electrochemical apparatus, and an accommodation space disposed        between the inlet and the outlet,        wherein the electrochemical double-cell plates are disposed in        the accommodation space and separated from each other to form at        least one channel, and wherein the oxygen-rich combustion waste        gas flows through the channels and contacts first reactive sides        and second reactive sides in the channels.

The electrochemical double-cell plate for exhaust emissions control ofthe present invention features a simple fabrication process. Thesubstrate is used as the basic structure, and the solid-state oxidelayer, the cathode layer and the boundary layer are sequentiallyoverlaid on the substrate. The substrate not only carries thesolid-state oxide layer and the cathode layer but also has a reducingcapability and functions as an anode. The substrate is a simple planarstructure, distinct from the honeycomb structure of the conventionalelectrocatalytic honeycomb apparatus, which is hard to fabricate andexpensive. Therefore, the present invention has an advantage of lowcost. The electrochemical double-cell plates for exhaust emissionscontrol of the present invention can be installed in an accommodationspace and separated from each other to form channels for the oxygen-richcombustion waste gas. The channels of the present invention are lesslikely to be blocked by particles. Therefore, the electrochemicalapparatus using the electrochemical double-cell plates of the presentinvention can process waste gas having a higher concentration of dust.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing an electrochemicaldouble-cell plate for exhaust emissions control according to a firstembodiment of the present invention.

FIG. 2 is a sectional view taken along Line A-A of FIG. 1.

FIG. 3 is a sectional view schematically showing an electrochemicaldouble-cell plate for exhaust emissions control according to a secondembodiment of the present invention.

FIG. 4 is a perspective view schematically showing an electrochemicaldouble-cell plate for exhaust emissions control according to a thirdembodiment of the present invention.

FIG. 5 is a sectional view taken along Line B-B of FIG. 4.

FIG. 6 is a perspective view schematically showing an electrochemicalapparatus for exhaust emissions control according to a fourth embodimentof the present invention.

FIG. 7 is a perspective view schematically an electrochemical apparatusfor exhaust emissions control according to a fifth embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The technical contents of the present invention will be described indetail in cooperation with the drawings below.

The present invention discloses an electrochemical double-cell plate forexhaust emissions control, which is used to purify an oxygen-richcombustion waste gas. In the present invention, the oxygen-richcombustion waste gas is referred to waste gas containing sulfur oxides(SO_(x)), nitrogen oxides (NO_(x)), carbon monoxide (CO), hydrocarbons(HCs), and particulate matters (PMs). The oxygen-rich combustion wastegas may be but is not limited to be the waste gas emitted bymotorcycles, automobiles, factories or power plants, or biogas. Below,the oxygen-rich combustion waste gas emitted by power plants is used asthe exemplification of the oxygen-rich combustion waste gas.

Refer to FIG. 1 and FIG. 2 respectively a perspective view schematicallyshowing an electrochemical double-cell plate for exhaust emissionscontrol according to a first embodiment of the present invention and asectional view taken along Line A-A of FIG. 1. The electrochemicaldouble-cell plate 10 for exhaust emissions control of the presentinvention is used to purify an oxygen-rich combustion waste gas 20 andcomprises a substrate 11, a solid-state oxide layer 12, a boundary layer13 and a cathode layer 14. The substrate 11 includes an outer surface111. The outer surface 111 has a top surface 112, a bottom surface 113opposite the top surface 112, and a side surface 114 joined with the topsurface 112 and the bottom surface 113. The substrate 11 is made of ametal or an alloy and has a reducing capability. In the firstembodiment, both the top surface 112 and the bottom surface 113 extendparallel and horizontally to make the substrate 10 a plate. In additionto carrying the solid-state oxide layer 12 and the cathode layer 14, thesubstrate 10 also function as an anode because of its reducingcapability.

The solid-state oxide layer 12 covers the top surface 112 and the bottomsurface 113. The solid-state oxide layer 12 has a first compactmicrostructure. The boundary layer 13 covers the side surface 111. Theboundary layer 13 has a second compact microstructure and cooperateswith the solid-state oxide layer 12 to seal the outer surface 111 of thesubstrate 11 so as to maintain the reducing capability of the substrate11. The solid-state oxide layer 12 is made of a fluorite-structure metaloxide or a perovskite-structure metal oxide, such as fluorite-structureyittria stabilized zirconia, fluorite-structure stabilized zirconia,fluorite-structure gadolinia-doped ceria (GDC), fluorite-structure dopedceria, perovskite-structure strontium/magnesium-doped lanthanum gallate(LSGM). The boundary layer 13 is made of glass or ceramic.

The cathode layer 14 covers the solid-state oxide layer 12. The cathodelayer 14 contacts the oxygen-rich combustion waste gas 20 and has anoxidizing environment. The cathode layer 14 is made of a porous materialand has a lot of pores. The porous material is selected from a groupincluding perovskite-structure metal oxides, fluorite-structure metaloxides, metal-added perovskite-structure metal oxides, and metal-addedfluorite-structure metal oxides, such as perovskite-structure lanthanumstrontium cobalt oxides, lanthanum strontium manganese oxides,combinations of lanthanum strontium manganese oxides and yittria-dopedceria, and combinations of lanthanum strontium manganese oxides andgadolinia-doped ceria.

In the present invention, the reducing capability of the substrate 11and the oxidizing environment of the cathode layer 14 generate anelectromotive force between the substrate 11 and the cathode layer 14.Thereby, the cathode layer 14 has a first reactive side 141 and a secondreactive side 142, which contact the oxygen-rich combustion waste gas 20and respectively correspond to the top surface 112 and the bottomsurface 113 of the substrate 11. The electromotive force enables theoxygen-rich combustion waste gas to undertake a decomposition reactionon the first reactive side 141 and the second reactive side 142 togenerate sulfur vapor, oxygen and nitrogen. Thus, the waste gas ispurified. In the present invention, the double cells of “electrochemicaldouble-cell plate for exhaust emissions control” are referred to theelectrochemical cell, which is formed by the top surface 112 of thesubstrate 11, the solid-state oxide layer 12 and the cathode layer 14,and the electrochemical cell, which is formed by the bottom surface 113of the substrate 11, the solid-state oxide layer 12 and the cathodelayer 14. The practical operations and chemical reactions of the presentinvention will be described below.

Refer to FIG. 3 a sectional view schematically showing anelectrochemical double-cell plate for exhaust emissions controlaccording to a second embodiment of the present invention. In the secondembodiment, the electrochemical double-cell plate 10 for exhaustemissions control of the present invention further comprises aninterface layer 15 and a powder layer 16. The interface layer 15 isdisposed between the solid-state oxide layer 12 and the cathode layer 14to enhance the connection of the solid-state oxide layer 12 and thecathode layer 14. The interface layer 15 is made of a fluorite-structuremetal oxide or perovskite-structure metal oxide, such asfluorite-structure gadolinia-doped ceria (GDC). The powder layer 16 isdisposed between the outer surface 111 of the substrate 11 and thesolid-state oxide layer 12 and functions as a reducing material. Thepowder layer 16 fully contacts the substrate 11 and the solid-stateoxide layer 12 and effectively enhances the interaction of the substrate11 and the solid-state oxide layer 12. In other words, the powder layer16 improves the reducing contact of the substrate 11 and the solid-stateoxide layer 12, enhances the reducing capability of the anode sides(i.e. the top surface 112 and the bottom surface 113), and thus favorscreation of the electromotive force.

Refer to FIG. 4 and FIG. 5 respectively a perspective view schematicallyshowing an electrochemical double-cell plate for exhaust emissionscontrol according to a third embodiment of the present invention and asectional view taken along Line B-B of FIG. 4. In the third embodiment,a plurality of upper recesses 1121 and a plurality of upper protrusions1122, each of which neighbors two upper recesses 1121, are distributedhorizontally on the top surface 112; a plurality of lower recesses 1131and a plurality of lower protrusions 1132, each of which neighbors twolower recesses 1131, are distributed horizontally on the bottom surface113. Because of the wave-like design of the substrate 11, theelectrochemical double-cell plate 10 of the third embodiment has largerarea of the first reactive side 141 and the second reactive side 142 ofthe cathode layer 14 than those of the first and second embodimentsunder the condition that the electrochemical double-cell plates 10 haveidentical length and width. Therefore, the electrochemical double-cellplate 10 of the third embodiment can process the oxygen-rich combustionwaste gas at a higher efficiency.

Refer to FIG. 6 a perspective view schematically showing anelectrochemical apparatus for exhaust emissions control according to afourth embodiment of the present invention. The electrochemicalapparatus for exhaust emissions control comprises a plurality ofelectrochemical double-cell plates 10 and a frame 30. The frame 30includes an inlet 31 allowing the oxygen-rich combustion waste gas 20 toflow into the electrochemical apparatus, an outlet 32 allowing theoxygen-rich combustion waste gas 20 to flow out of the electrochemicalapparatus, and an accommodation space 33 disposed between the inlet 31and the outlet 32 and receiving the electrochemical double-cell plates10. At least one channel 34 is formed between the electrochemicaldouble-cell plates 10. The oxygen-rich combustion waste gas 20 flowsinto the channels 34 via the inlet 31, contacts the first reactive sides141 and the second reactive sides 142 in the channels 34 and then flowsout of the electrochemical apparatus from the outlet 32. In theembodiment shown in FIG. 6, the electrochemical double-cell plates 10are arranged in a way that the planes of the first reactive side 141 andthe second reactive side 142 are parallel to the flow direction of theoxygen-rich combustion waste gas 20, whereby the oxygen-rich combustionwaste gas 20 has the maximum contact area with the first reactive side141 and the second reactive side 142. The design of the fourthembodiment makes the oxygen-rich combustion waste gas 20 contact thesurfaces of a plurality of first reactive side 141 and a plurality ofsecond reactive sides 142. Thus, the waste gas can be purified moreefficiently.

Refer to FIG. 7 a perspective view schematically an electrochemicalapparatus for exhaust emissions control according to a fifth embodimentof the present invention. In the fifth embodiment, the electrochemicaldouble-cell plates 10 fabricated with the wave-like substrates 11 andthe electrochemical double-cell plates 10 fabricated with the planarsubstrates 11 are used jointly and arranged alternately. A plurality ofchannels is thus formed between the electrochemical double-cell plates10. The flow of the oxygen-rich combustion waste gas 20 in the fifthembodiment is shown in FIG. 7. Under the condition that theelectrochemical apparatuses have an identical volume, the contact areaof the oxygen-rich combustion waste gas 20 and the cathode layer 14 islarger in the fifth embodiment than in the fourth embodiment shown inFIG. 6. Therefore, electrochemical apparatus of the fifth embodiment hasa higher efficiency.

The principle and chemical reactions of processing the oxygen-richcombustion waste gas 20 in the electrochemical double-cell plate 10 andelectrochemical apparatus for exhaust emissions control will bedescribed thereinafter. Below, the electrochemical double-cell plate 10for exhaust emissions control is used to demonstrate the principle andchemical reaction of the present invention. The persons skilled in theart should be able to apply the principle to the electrochemicalapparatus for exhaust emissions control. As mentioned above, theoxygen-rich combustion waste gas 20 contains sulfur oxides, nitrogenoxides, carbon monoxide, hydrocarbons, and particulate matters. Thepurification reactions mainly include three portions: the reaction ofeliminating nitrogen oxides, the reaction of eliminating carbonmonoxide, hydrocarbons and particulate matters, and the reaction ofeliminating sulfur oxides.

Elimination of Nitrogen Oxides

The nitrogen oxides mainly include nitrogen monoxide (NO) and nitrogendioxide (NO₂). Nitrogen monoxide is decomposed into nitrogen and oxygenin the first reactive side 141 and the second reactive side 142 of thecathode layer 14; the reaction thereof is expressed by Formula (a):

2NO→N₂±O₂  (a)

Nitrogen dioxide is decomposed into nitrogen monoxide and oxygen in thefirst reactive side 141 and the second reactive side 142 of the cathodelayer 14; the reaction thereof is expressed by Formula (b):

2NO₂→2NO+O₂  (b)

The nitrogen monoxide generated in Reaction (b) (the reaction expressedby Formula (b)) is further decomposed into nitrogen and oxygen in thefirst reactive side 141 and the second reactive side 142 of the cathodelayer 14.

The reducing capability of the substrate 11 and the oxidizingenvironment of the cathode layer 14 generate different equilibriumoxygen partial pressures respectively in the substrate 11 and thecathode layer 14 and generate an electromotive force (emf) between thesubstrate 11 and the cathode layer 14. The electromotive force drivesthe nitrogen oxides of the oxygen-rich combustion waste gas to decomposeand generate nitrogen and oxygen. The electromotive force is generatedaccording to the following principle:

emf=[(RT)/(4F)]·ln [(P _(O2|Cathode))/(P _(O2|Anode))]  (c)

wherein R is the gas constant, T the absolute temperature, F the Faradayconstant, and P_(O2) the equilibrium oxygen partial pressure. Thesubstrate 11, which is made of a metal or an alloy, is a reducingmaterial, generating an environment of a very low equilibrium oxygenpartial pressure in the anode and thus having a greater electromotiveforce. Different reducing compounds lead to different equilibrium oxygenpartial pressures in the anode and thus generate different electromotiveforces. In the cathode, different concentrations of oxygen correspond todifferent equilibrium oxygen partial pressures and generate differentelectromotive forces. In other words, the larger the concentration ofoxygen of the oxygen-rich combustion waste gas 20 in the cathode, thegreater the electromotive force; the greater the electromotive force,the higher the reaction rate of decomposition of nitrogen oxides.

Elimination of Carbon Monoxide, Hydrocarbons and Particulate Matters

As the oxygen-rich combustion waste gas 20 is abundant of oxygen, thecathode layer 14 can catalyze oxidizing reactions to convert carbonmonoxide, hydrocarbons and particulate matters into harmless gases. Thecarbon monoxide can be oxidized into carbon dioxide; the hydrocarbonsand the particulate matters (containing carbon) can be oxidized intocarbon dioxide and water; the reactions can be respectively expressed byFormulae (d)-(f):

2CO+O₂→2CO₂  (d)

HCs+O₂→H₂O+CO₂  (e)

C+O₂→CO₂  (f)

Therefore, the present invention can uses the electromotive force todrive decomposition reactions to eliminate nitrogen oxides and uses theoxidizing reactions to eliminate carbon monoxide, hydrocarbons andparticulate matters. Thus, the present invention can effectively removethe harmful components in the oxygen-rich combustion waste gas 20.

Elimination of Sulfur Oxides

The oxygen-rich combustion waste gas 20 is cooled down to a temperatureof lower than 200° C. and then passes through the electrochemicaldouble-cell plates 10 for exhaust emissions control. In theelectrochemical double-cell plates 10, the reducing capability of thesubstrates 11 and the oxygen-containing environment of the oxygen-richcombustion waste gas 20 generate an electromotive force between thesubstrates 11 and the cathode layers 14. The electromotive force drivesthe sulfur oxides of the oxygen-rich combustion waste gas 20 todecompose into sulfur vapor and oxygen in the cathode layers 14. Afterleaving the electrochemical double-cell plates 10, the sulfur vapor iscooled down to form solid-state sulfur crystals. Then, the sulfurcrystals are collected. The abovementioned reactions can be respectivelyexpressed by Formulae (g)-(i):

SO₃→SO₂+O₂  (g)

2SO₂→S_(2(g))+2O₂  (h)

4S_(2(g))→S_(8(g))  (i)

The sulfur oxides of the oxygen-rich combustion waste gas 20 are mainlysulfur dioxide (SO₂) and a trace amount of sulfur trioxide (SO₃). Whilecontacting the cathode layer 14, the sulfur trioxide (SO₃) of theoxygen-rich combustion waste gas 20 undertakes a reaction expressed byFormula (g) and decomposes into sulfur dioxide (SO₂) and oxygen (O₂).The sulfur dioxide (SO₂) originally in the oxygen-rich combustion wastegas 20 and the sulfur dioxide (SO₂) generated by the decomposition ofsulfur trioxide (SO₃) undertakes a reaction expressed by Formula (h) anddecomposes into sulfur vapor (S₂) and oxygen (O₂). In theelectrochemical double-cell plates 10, the sulfur vapor of S₂ mayfurther combine to form the sulfur vapor of S₈, as shown by Formula (i).At a temperature of lower than 200° C., S₂ may fully combine to form S₈.After leaving the electrochemical double-cell plates 10, the sulfurvapor of S₈ is cooled down to form solid-state sulfur crystals. Thus,the sulfur oxides are eliminated from the oxygen-rich combustion wastegas 20. Then, the sulfur crystals are collected.

In conclusion, the present invention proposes an electrochemicaldouble-cell plate for exhaust emissions control, which features a simplefabrication process, wherein a substrate is used as the basic structure,and the solid-state oxide layer, the cathode layer and the boundarylayer are sequentially overlaid on the substrate. The substrate not onlycarries the solid-state oxide layer and the cathode layer but also has areducing capability and functions as an anode. The substrate is a simpleplanar structure, distinct from the honeycomb structure of theconventional electrocatalytic honeycomb apparatus, which is hard tofabricate and expensive. Therefore, the present invention has anadvantage of low cost. The electrochemical double-cell plates forexhaust emissions control of the present invention can be installed inan accommodation space and separated from each other to form channelsfor the oxygen-rich combustion waste gas. The channels of the presentinvention are less likely to be blocked by particles. Therefore, theelectrochemical apparatus using the electrochemical double-cell platesof the present invention can process waste gas having a higherconcentration of dust.

What is claimed is:
 1. An electrochemical double-cell plate for exhaustemissions control, which is used to purify an oxygen-rich combustionwaste gas and comprises a substrate made of a metal or an alloy, havinga reducing capability, and including an outer surface, wherein the outersurface has a top surface, a bottom surface opposite the top surface,and a side surface joined with the top surface and the bottom surface; asolid-state oxide layer covering the top surface and the bottom surfaceand having a first compact microstructure; a boundary layer covering theside surface, having a second compact microstructure, and cooperatingwith the solid-state oxide layer to seal the outer surface of thesubstrate; and a cathode layer covering the solid-state oxide layer,made of a porous material, contacting the oxygen-rich combustion wastegas, and having an oxidizing environment, wherein the oxidizingenvironment and the reducing capability generate an electromotive forcebetween the substrate and the cathode layer and make the cathode layerhave a first reactive side and a second reactive side respectivelycorresponding to the top surface and the bottom surface of thesubstrate, and wherein the electromotive force enables sulfur oxides andnitrogen oxides of the oxygen-rich combustion waste gas to undertakedecomposition reactions on the first reactive side and the secondreactive side to generate sulfur vapor, oxygen and nitrogen.
 2. Theelectrochemical double-cell plate for exhaust emissions controlaccording to claim 1, wherein the solid-state oxide layer is made of amaterial selected from a group including fluorite-structure metaloxides, perovskite-structure metal oxides, and combinations thereof. 3.The electrochemical double-cell plate for exhaust emissions controlaccording to claim 1, wherein the boundary layer is made of glass orceramic.
 4. The electrochemical double-cell plate for exhaust emissionscontrol according to claim 1, wherein the cathode layer is made of amaterial selected from a group including perovskite-structure metaloxides, fluorite-structure metal oxides, metal-addedperovskite-structure metal oxides, metal-added fluorite-structure metaloxides, and combinations thereof.
 5. The electrochemical double-cellplate for exhaust emissions control according to claim 1 furthercomprising an interface layer, which is disposed between the solid-stateoxide layer and the cathode layer to enhance connection of thesolid-state oxide layer and the cathode layer.
 6. The electrochemicaldouble-cell plate for exhaust emissions control according to claim 5,wherein the interface layer is made of a material selected a groupincluding fluorite-structure metal oxides, perovskite-structure metaloxides, and combinations thereof.
 7. The electrochemical double-cellplate for exhaust emissions control according to claim 1, wherein boththe top surface and the bottom surface extend parallel and horizontallyto make the substrate a plate.
 8. The electrochemical double-cell platefor exhaust emissions control according to claim 1, wherein a pluralityof upper recesses and a plurality of upper protrusions each neighboringtwo upper recesses are distributed horizontally on the top surface; aplurality of lower recesses and a plurality of lower protrusions eachneighboring two lower recesses are distributed horizontally on thebottom surface.
 9. The electrochemical double-cell plate for exhaustemissions control according to claim 1 further comprising a powderlayer, which is disposed between the outer surface of the substrate andthe solid-state oxide layer, and which is made of a metal or an alloyand enhances interaction of the substrate and the solid-state oxidelayer.
 10. An electrochemical apparatus for exhaust emissions control,which is used to purify an oxygen-rich combustion waste gas andcomprises a plurality of electrochemical double-cell plates for exhaustemissions control according to claim 1; and a frame including an inletallowing the oxygen-rich combustion waste gas to flow into theelectrochemical apparatus, an outlet allowing the oxygen-rich combustionwaste gas to flow out of the electrochemical apparatus, and anaccommodation space disposed between the inlet and the outlet, whereinthe electrochemical double-cell plates are disposed in the accommodationspace and separated from each other to form at least one channel, andwherein the oxygen-rich combustion waste gas flows through the channelsand contacts first reactive sides and second reactive sides in thechannels.